The present invention concerns an apparatus for changing tools mounted within a tapered tool holder. The invention has particular application for use with an automatic machining center that includes a tool magazine to retain tools for use in subsequent machining operations.
A typical numerically controlled machine tool system includes a machining center having a tool magazine and a tool changing mechanism. The mechanism removes a particular tool from the machining spindle and replaces it with a different tool extracted from the tool magazine. With machining centers of this type, a plurality of machining operations are conducted, which can require a like number of different machine tools. Thus, the tool magazine or rack stores the plurality of tools needed for on-demand usage.
In the development of modern machining centers, considerable focus has been placed on the tool changing mechanism--i.e., the device that extracts a particular tool from the magazine and places it within the operating spinal at the machining location. For instance, the automatic tool changer of Hague et al., is depicted in U.S. Pat. No. 3,844,028, is typical of the automatic tool changing mechanisms.
The tool magazine comes in a variety of forms. Typically, the tools are mounted on a movable component of the magazine that is integrated into the numeric control system of the machining center. The magazine can be controlled to move a desired tool to a pre-determined location to be extracted by the automatic tool changing mechanism. One type of tool magazine is shown in FIG. 1. In particular, a magazine 10 includes a plurality of tool pockets 12 that are configured to firmly grasp a tool holder. The magazine 10 depicted in FIG. 1 is a turret type magazine in which the tool pockets 12 are interconnected by a drive chain 14 or similar pocket positioning mechanism. The chain is wound around a hub 15 and is driven by a motor under direction from the numeric control system. In operation, the drive chain 14 can be incrementally driven to position a specific tool pocket 12 at the tool changing location. The magazine 10 also includes a housing 17 that surrounds and supports the tool pockets 12, the driving mechanism 14 and hub 15.
A typical tool pocket 12 is depicted in FIG. 2. In particular, the pocket is configured to support a tapered tool holder 20. It is understood that the tool holder 20 can engage and support a variety of machine tools, such as drill or a milling bit. The tool holder 20 is of a standard configuration. Specifically, the holder 20 can include a tapered body 22 that can conform to a variety standards, such as the ANSI/DIN standard. For example, the body 22 can be a 20, 25, 30 , 45, 50 or a 60 taper. The tool holder 20 terminates at one end in an enlarged retention knob 21. At the opposite end, the holder defines a flange 23 that can be engaged by the automatic tool changing mechanism to extract the tool holder 20 from the tool pocket 12 and engage the holder in the machining spindle.
The tool holder 20 is retained within the tool pocket 12 by a mechanism configured to engage the retention knob 21. In a typical system, a plurality of retention balls 27 are held within radial bores that intersect the interior of the pocket. More particularly, the retention balls 27 contact the retention knob 21 of the tool holder 20. Each retention ball 27 is held in position by a retention spring 28 disposed within the radial bore. The retention springs 28 are calibrated to provide a particular spring force (acting in the direction of the arrows) bearing against the retention knob 21 of the tool holder 20. This retention force must be overcome to remove the tool holder 20 from the pocket 12. Likewise, the spring force must be overcome to push the tool holder 20 into the pocket and past the retention balls 27. Of course, the force required to push in or pull out the tool holder is a function of the force required to compress the retention springs 28 as the retention balls 27 are pushed aside by the knob 21.
It is this push-in/insertion and pull-out/extraction force that is addressed by the present invention. More specifically, for larger taper tool holders 20, such as 45 taper and beyond, the retention spring force generated by the retention springs 28 is too strong to be manually overcome. Even smaller ANSI/DIN tapers can also be very difficult to overcome by manual manipulation of the tool holder 20. One complication is that the tool holders 20 can themselves be very heavy, in some instances weighing as much as 35 pounds. Thus, even if the retention spring force could be manually overcome, the weight of the tool holder 20 makes it unwieldy and difficult to manipulate.
In some machining center installations, the particular tools are changed within the magazine relatively infrequently. However, in higher production facilities, a machine operator may be regularly required to remove a tool holder from the magazine and insert a new tool holder. For instance, the machining tool itself may break, obviously requiring replacement. In addition, program modifications to the numerically controlled machining sequence may necessitate tool changes. When smaller machines are used, the magazine may not have the capacity to hold enough different tools to complete a particular machining sequence. In all of these instances the machine operator must be able to readily change out a particular tool from the magazine 10.
Thus far, no adequate apparatus is available that allows ready and easy change-out or replacement of machine tools within a magazine. In one prevalent approach, the machine operator simply cycles the requisite tool through the automatic tool changer operation. With this approach, the operator uses the tool changer to extract the target tool holder 20 from the magazine 10 and carry it over to the machine spindle. The tool holder can then be removed from the spindle by the operator and replaced with another tool holder, after which the automatic tool changer then returns the new holder to the magazine. Of course, this procedure requires significant down time because the machining spindle is used to effect the tool change, taking the machining center temporarily out of production.
An optimum approach would be to permit manual replacement of particular tools within a magazine. A further optimum condition would be to permit tool changes while the machining center is performing its machining function. In most numerically controlled machines, the tool magazine is isolated from the machining location, and can be shielded even further to protect the operator as he accesses the magazine, so this simultaneous activity can be accommodated.